1. Field of the Invention
The present invention relates to a lead frame and a resin-sealed semiconductor device using the lead frame.
2. Description of the Related Art
Conventionally, semiconductor devices mainly use a lead frame because it can be manufactured at high productivity and low cost as a wiring member for connecting the semiconductor device with an external circuit.
FIG. 17 is a top view of a resin-sealed semiconductor device using a conventional lead frame and FIG. 18 is a sectional view taken along the line XVIII--XVIII in FIG. 17 in the middle of the resin sealing process. In FIGS. 17 and 18, a semiconductor element 1 is mounted on a die pad 2 of a lead frame. The die pad 2 is supported by two suspension leads 3 from two directions. The semiconductor element 1 is secured to the die pad 2 by a bonding material 4. The semiconductor device is sealed by a sealing resin 5. As shown in FIG. 18, the flow length 6 of the sealing resin 5 on the semiconductor element 1 during the sealing resin process is longer than the flow length 7 of the sealing resin 5 under the die pad 2. Then, the semiconductor element 1 and die pad 2 are entirely sealed with the resin to form a semiconductor package 8. The semiconductor element 1 is held by the die pad 2 of the lead frame. An electrode formed on the semiconductor element 1 is bonded with an electrode of the lead frame by a thin metallic wire or the like and then, the thermosetting sealing resin 5 is injected and cured to form the semiconductor package 8. In FIG. 18, there is a difference equivalent to the thickness of the die pad 2 between the injection channel widths of the sealing resin 5 at the top and the bottom of the semiconductor element 1. Therefore, when injecting the resin, a difference is produced between the flow length 6 of the sealing resin 5 on the semiconductor element 1 and the flow length 7 of the sealing resin 5 under the die pad 2.
FIG. 19 is a top view of a resin-sealed semiconductor device using another conventional lead frame and FIG. 20 is a sectional view of the portion taken along the line XX--XX of FIG. 19 during the resin sealing process. In FIGS. 19 and 20, a suspension lead 9 of a lead frame supports a die pad 2 from four directions. Other structures are the same as those in FIGS. 17 and 18.
A resin-sealed semiconductor device using a conventional lead frame is constituted as described above. A lead frame is decreased in thickness as a semiconductor device is decreased in size and thickness and, moreover, a semiconductor element is increased in size as the semiconductor device is improved in function. Furthermore, there are problems that not only the lead frame but also semiconductor device components are deformed due to various stresses received in fabricating the semiconductor device and thereby, the quality and fabrication yield of semiconductor devices are deteriorated.
Particularly when sealing a semiconductor element with a resin by injection-molding and thermally curing a thermosetting resin in fabricating a semiconductor device, the thickness of the sealing resin is decreased due to a decrease in the semiconductor device thickness and a sealing-resin injection channel is narrowed in the thermosetting-resin injection molding process. Moreover, a difference in thickness equivalent to a die pad is produced between the channel thicknesses at the top and the bottom (that is, the bottom of the die pad 2) of a semiconductor element and, thereby, the sealing-resin flow velocity on the semiconductor element 1 is different from the sealing-resin flow velocity under the die pad 2. That is, as shown in FIG. 18, a difference is produced between the sealing-resin flow length 6 on the semiconductor element 1 and the sealing-resin flow length 7 under the die pad 2. Moreover, a difference is produced between the pressure applied to the semiconductor element 1 from the sealing resin 5 at the top and the pressure applied to the die pad 2 from the sealing resin 5 at the bottom. As a result, deformation of a lead frame having a semiconductor element and a die pad is induced. Furthermore, in the process for thermally curing the sealing resin 5, warpage or deformation occurs in a semiconductor package due to cured resin contraction because the amount of sealing resin on the semiconductor element 1 is different from the amount of sealing resin under the semiconductor element by an amount equivalent to the volume of the die pad 2.